Switches or switch elements are interconnected within a communication network in order to direct data from one point to another point within the network. Typically, each switch element has a plurality of inputs and a corresponding plurality of outputs. Network connections can be coupled to each of the switch element inputs and outputs, so that data carried on any input line of a switch element can be switched to any output line on the same switch element. Networks, however, do not remain fixed. Rather, frequently, some network connections are added, while others are dropped. Alternatively, data previously intended for one switch output line may be required to be shifted to another output line. In response to such changes, a switch element in a network must be appropriately reconfigured or rearranged.
Switching events may occur, which would require the network connections across the switch element to be manipulated. Due to the number of connections across a single switching element, compensating for a switching event can be a complex and computationally intensive procedure. Examples of switching events include instances when network connections are added to a switch element already in use or instances when one of the links between network elements fails and another route through the network element is needed.
When switching events require new connections to be formed, conventional switch elements must reconfigure the entire switch element. Many switch elements comprise devices, which are grouped into one of three stages of a three stage Clos array (e.g., within an ingress stage, a center stage or an egress stage). Typically, in response to switching events all of the switching devices (including those related to connections that are not directly affected by the switching event) within each of the stages of the array need to be reconfigured to form new connections through the switch element.
A conventional switch element in such a rearrangeable, non-blocking switching configuration typically requires considerable computational resources to accomplish reconfiguration of the switching devices within the switch element at the speed required by such applications as SONET. For example, if a switch element fails to compensate for switching events in less than 60 ms, the occurrence of the switching event may become noticeable to an end-user, which in many instances is viewed as an unacceptable result. Due to the complexities of the algorithms used to establish such reconfigurations for switch elements, it can become even more difficult to repeatedly execute control algorithms in a manner that ensures switching events are compensated for while being transparent to the end-user.
Accordingly, there is a need for a new switching control mechanism in a three stage rearrangeable, non-blocking Clos network, which provides for faster rearrangement performance in response to switching events.